Silent myocardial ischemia in patients with coronary artery disease is a condition which is characterized by an imbalance between the heart's requirement for oxygen and the supply of oxygen. When transient, this imbalance between supply and demand results in chest pain or angina, but it is often silent. Episodes of silent ischemia can be detected by continuous electrocardiographic monitoring of the ST segment using Holter monitoring. Some reports have suggested that the presence of silent ischemia on Holter identifies a high risk subgroup of patients with coronary artery disease. We have investigated the 2 year outcome of the presence of silent ischemia in an anatomic and functional low-risk subset of 95 patients with coronary artery disease and compared them with 17 patients in a high risk subset (those who had severe multivessel coronary artery disease and/or left ventricular dysfunction). Almost half the patients in the low risk and two-thirds of the patients in the high risk subsets had silent ischemia during daily activities. Myocardial infarction or unstable angina occurred in 2.5% of Holter positive patients and 11% of patients who were Holter negative in the low risk subset. The difference was not statistically significant. However, in the high risk subset, 45% of patients had events in the Holter positive group. Thus, ambulatory ischemia indicates a worse outcome only in patients who are conventionally known to be in high risk, and although frequently present in low risk subsets, it is not associated with an adverse medium term prognosis.